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Not a big deal, if you have some time and real estate. Assume that you know about noons and solstices, and can catch either by watching a shadow of a post. During a summer solstice, position two posts along the line of the rays / shadow; the longer the better. Watch the sun hit the same line during a winter solstice. Along the way, notice when, relative to the exact solstice moment, is the noon. Sometimes you'll miss the exact solstice moment because the sun will be below horizon. A dozen or two years of watching and recording should show you that the positions of the sun during solstices, and the time oof the exact solstice positions relative to the noon, roughly repeat every 4 years. For bonus points, mark the positions of bright stars, like Sirius, Vega, Arcturus, etc, and notice how they repeat their patterns on solstice days / nights. They will repeat every 365 days approximately (like solstices, yearly), and every 1641 days exactly (4 years). This all takes a large, flat, undisturbed surface to put posts on, to mark angles. Not a lot of work, and could fit in one lifetime pretty well, given some prior ideas of watching the sky and measuring angles. Of course, as you improve your instruments, you will notice how your neat approximations actually are imprecise, etc, and you'll have to invent a Gregorian calendar to spread the error more uniformly :) |